U.S. patent application number 10/708717 was filed with the patent office on 2005-09-22 for omni voltage direct current power supply.
Invention is credited to Baxter, Kevin C., Fisher, Ken S., Holmes, Fred H..
Application Number | 20050207196 10/708717 |
Document ID | / |
Family ID | 34377707 |
Filed Date | 2005-09-22 |
United States Patent
Application |
20050207196 |
Kind Code |
A1 |
Holmes, Fred H. ; et
al. |
September 22, 2005 |
OMNI VOLTAGE DIRECT CURRENT POWER SUPPLY
Abstract
A battery operated LED lighting apparatus including: a battery
outputting a battery voltage; a light emitting diode or array of
light emitting diodes; and a power supply including a boost
regulating circuit. The power supply being in communication with
the battery and the light emitting diodes such that a constant
voltage or constant current is supplied to the light emitting
diodes as the battery discharges and the battery voltage falls
below the output voltage. In a preferred embodiment the power
supply further includes a buck regulator to maintain the proper
output voltage when the battery voltage is greater than the output
voltage.
Inventors: |
Holmes, Fred H.; (Cleveland,
OK) ; Baxter, Kevin C.; (Saugus, CA) ; Fisher,
Ken S.; (Los Angeles, CA) |
Correspondence
Address: |
KEN FISHER
5521 CLEON AVE.
NORTH HOLLYWOOD
CA
91601
US
|
Family ID: |
34377707 |
Appl. No.: |
10/708717 |
Filed: |
March 19, 2004 |
Current U.S.
Class: |
363/126 |
Current CPC
Class: |
H05B 45/10 20200101;
H05B 45/14 20200101; H05B 45/38 20200101; H05B 45/375 20200101 |
Class at
Publication: |
363/126 |
International
Class: |
H01K 007/00 |
Claims
1. A battery operated led lighting apparatus comprising: a battery
outputting a battery voltage; a light emitting diode; and a power
supply including a boost regulating circuit, said power supply in
communication with said battery and said light emitting diode such
that a constant voltage is supplied to said light emitting diode as
said battery discharges, wherein over at least a portion of said
discharge cycle said constant voltage is higher than said battery
voltage.
2. The battery operated LED lighting apparatus of claim 1 wherein
said light emitting diode comprises a plurality of groups, said
groups connected in parallel and each group of said plurality of
groups comprising a plurality of light emitting diodes connected in
series.
3. The battery operated LED lighting apparatus of claim 2 wherein
said each group further includes a ballasting device connected in
series with said plurality of light emitting diodes connected in
series.
4. The battery operated LED lighting apparatus of claim 3 wherein
said ballasting device is a resistor.
5. The battery operated LED lighting device of claim 1 wherein said
power supply further comprises a buck regulator and wherein over a
portion of said discharge cycle said battery voltage is greater
than said constant voltage and said buck regulator is operative to
regulate said battery voltage at said constant voltage.
6. A battery operated LED lighting apparatus comprising: a battery
outputting a battery voltage; a light emitting diode; a power
supply including a boost regulating circuit, said power supply in
communication with said battery to produce an output voltage to
said light emitting diode such that a constant current is supplied
to said light emitting diode as said battery discharges wherein
over at least a portion of said discharge cycle said output voltage
is higher than said battery voltage.
7. The battery operated LED lighting apparatus of claim 6 wherein
said light emitting diode comprises a plurality of groups, said
groups being connected in parallel and each group of said plurality
of groups comprising a plurality of light emitting diodes connected
in series.
8. The battery operated LED lighting apparatus of claim 7 wherein
said each group further includes a ballasting device connected in
series with said plurality of light emitting diodes connected in
series.
9. The battery operated LED lighting device of claim 6 wherein said
power supply further comprises a buck regulator and wherein over a
portion of said discharge cycle said battery voltage is greater
than said output voltage and said buck regulator is operative to
regulate said battery voltage at said output voltage to produce a
constant current through said light emitting diode.
Description
BACKGROUND OF INVENTION
[0001] The present invention relates to electronic power supplies.
More particularly, but not by way of limitation, the present
invention relates to a power supply which would provide a
pre-determined voltage output from batteries, which themselves
could vary in number, voltage or level of charge.
[0002] As will become apparent from the discussion below, there is
generally a need for a boost regulator for battery-operated devices
whereby the output voltage will remain constant over substantially
the entire discharge cycle of the battery. There are several areas
where this is especially true such as battery operated lighting
used in the motion picture and television industries and for
certain battery operated, motorized devices.
[0003] U.S. Pat. No. 6,246,184 issued to Salerno represents a step
in the right direction. Salerno discloses a boost regulator for a
conventional battery operated flashlight wherein, after the battery
voltage falls 15-20%, the boost regulator kicks in to provide a
substantially constant voltage until a major portion of the stored
battery energy has been consumed. While Salerno provides a marked
improvement for conventional hand-held flashlights, the
improvements are limited to devices where the initial battery
voltage is the same as the lamp voltage. In addition, the device of
Salerno is clearly drawn to conventional lamps, which employ a
filament. Such lamps are inefficient, not daylight balanced, and
somewhat fragile compared to alternative lamps.
[0004] Continuous arc xenon bulbs (hereinafter referred to as a
"xenon lamp") provide bright, stable, daylight balanced light at
power levels from a few watts up to tens of thousands of watts.
Such bulbs are widely accepted in architectural, entertainment, and
medical applications. Typically, such bulbs require a moderate DC
voltage (on the order of 12 to 50 volts) at a relatively high
current for steady-state operation. Some longer arc bulbs require
higher voltages. Thus, a ballast or power supply is normally
required for operation of a xenon bulb. Presently, xenon power
supplies may be logically divided into two distinct groups, those
that operate on line voltages and those that operate on batteries.
The line voltage versions are the larger and more recognizable
versions used in motion picture lighting, architectural, and night
sky based advertising. The battery versions are usually flashlights
of no more than 70 watts. While xenon flashlights do have boosting
circuits, they presently do not allow connection to anything other
than 12 volt batteries and the output voltage varies with input
voltage. These same flashlights operate from 13.2 volts, the fully
charged voltage of the 12 volt batteries, down to about 11 volts
where the flashlight shuts off. This leaves an enormous untapped
potential in the battery.
[0005] Car batteries, which are likewise nominally 12 volts,
generally have about 1 kilowatt-hour of capacity. If a car battery,
through a power supply, were used to power one of the larger
fixtures, battery life would be objectionably short. For example, a
fixture with a 4 kilowatt xenon bulb could only operate for 15
minutes. This is one reason no large xenon lights are battery
powered.
[0006] In addition, xenon lamps have a zener diode-like
characteristic in that, when a xenon lamp is operating, even small
changes in lamp voltage result in disproportionately large changes
in current. Accordingly, ballasting is typically employed to limit
the electrical current applied to a xenon lamp. Thus there exists a
need for a battery operated xenon power supply, which provides
ballasting of bulb current and allows a greater portion of a
battery's charge to be extracted before recharging than do present
systems.
[0007] Light Emitting Diode ("LED") lamps have traditionally been
used for indicators and displays but just recently have evolved
into primary illumination sources. This evolution has accompanied
the advent of new colors, and brighter LED lamps. Groups of these
new and powerful LEDs have recently been integrated into fixtures
and have become capable of lighting broad areas with useable levels
of light. These devices require a large DC source of power to
operate in a non-flickering mode. They are also very sensitive to
over-current conditions, which can easily destroy the devices. The
voltage required by these LED fixtures depends on the number of
individual LEDs that are connected in a series combination inside
the fixture. The voltage and current to these fixtures vary with
temperature and from device-to-device. Consequently they must be
ballasted or regulated to keep a steady output. At present, battery
based applications for LED fixtures are primarily for emergency
lighting. Initially these fixtures do an adequate job of
illuminating, but as the batteries run down, the light intensity
fades. This is one primary reason battery based LEDs are not
regularly used for illumination in motion picture and photography
lighting situations. Photography can't be precisely practiced with
slowly dimming light levels.
[0008] There have been a few attempts to run small LED devices on
batteries with simple series voltage regulators in-line with the
battery. These systems are very inefficient and when the battery
discharges even slightly, the circuit begins to dim because there
is not enough voltage in the battery to make up for the regulator
voltage drop as well as other losses. One could include a larger
number of batteries to provide more head room for the regulator,
but the higher voltages would cause efficiencies to drop even lower
due to increased heating of the regulator. Also the size and weight
of the batteries would become unmanageable.
[0009] In addition, there are numerous fields in which it is either
difficult to match a battery voltage to the requirements of an
appliance, or the appliance is intolerant of the diminishing
voltage of a draining battery. For example, motion picture and
television cameras generally work on rechargeable lead acid or
NiCad type batteries. These batteries are used until the voltage
drops from an initial 13.2 volts down to between 10 and 11 volts.
At that point there is an enormous potential of electricity left
but unusable in these batteries. Cameramen typically have multiple
sets of batteries used in rotation. Some in use, some being
charged, and some waiting as ready. Not only is this number of
batteries an expensive proposition, the management of this number
of batteries is time consuming, creates logistic nightmares and is
otherwise just generally problematic.
[0010] Direct current motors are often connected to batteries. This
type of configuration is generally used with motors for displays,
servos, hydraulic pumps, trolling motors, portable tools, and
vehicle-mounted winches. When used with motors, some battery
circuits are run through speed control circuits, but otherwise
connect directly to the battery. (Trucks and farm machinery have
the advantage of constantly recharging their batteries from a
running internal combustion engine). Even in this situation,
however, the battery voltage can lag during a high cycle use of the
motor. And of course, as the voltage goes down, so does the motor
speed, and/or torque. This is clearly evident when using a
battery-powered man-lift. As the battery fades, the lift's moving
ability becomes less and less until the operator has no choice but
to return to the ground, assuming, of course, that there is
sufficient power to lower the lift.
[0011] Many DC motor driven devices use multiple, series connected
batteries to raise the capacity of energy available, while
decreasing electrical current through motor, which will extend the
usage in both time and torque. The down side of this is that
companies often have to make similar and somewhat redundant
versions of a particular product line to operate at these different
voltages. Added to that, these similar versions may be accidentally
confused with one another and consequently connected to incorrect
voltages that may destroy the motor or its controller. These
multiple-battery configurations also have the added problem of the
weakest link. It is well known in the art that the weakest cell may
actually reverse charge during normal use, further lowering the
voltage available to the motor. As with a single battery, when a
the collective charge of a series of batteries is discharged to the
point where the motor's performance degrades, there is a great deal
of energy left in the batteries that can not be tapped by existing
techniques.
[0012] This problem can also be found in battery-operated tools
such as drills, saws, sanders, and the like. Well before the
battery charge is fully exhausted, but after the voltage has
dropped a few volts, the motors of such devices will not develop
enough torque to make the tools usable. As in other areas, spare
batteries are often kept on hand so that a set can be charging
while a set is in use, and perhaps, a charged set stands ready for
use. The investment in batteries can dwarf the investment in the
tool itself.
[0013] Thus it is an object of the present invention to provide a
battery operated electronic power supply, which can provide a
constant output voltage over a substantial portion of the battery
charge.
[0014] It is a further object of the present invention to provide a
battery operated electronic power supply, which provides a constant
power source for LED based illumination systems over a wide range
of battery voltages.
[0015] It is still a further object of the present invention to
provide a battery operated electronic power supply, which provides
a constant power source for DC motors.
[0016] It is yet a further object of the present invention to
provide a battery operated electronic power supply, which provides
a ballasted, constant power source for operating a xenon light.
SUMMARY OF INVENTION
[0017] The present invention provides an electronic power supply,
which provides a predetermined, steady state voltage to a
battery-operated appliance, such as a light or motor. The power
supply, powered by a variable number of batteries connected in
series, will provide a constant output voltage, regardless of the
number of batteries or the condition of their charge, until
substantially all of the battery charge has been depleted.
[0018] In one preferred embodiment, a ballasting DC-DC converter
includes: a boost regulator for providing a predetermined voltage;
and a ballasting circuit for providing efficient, precise control
of a bulb current in a xenon fixture. Those familiar with xenon
lamps will appreciate that the operation of such bulbs requires a
number of steps. First, with an un-struck lamp, a starting voltage
must be applied across the contacts of the lamp; typically at least
three or four times the operating voltage. Next an igniter pulse of
several thousand volts must be momentarily applied to the lamp to
start the arc. Finally, the voltage and current must be managed to
operate the lamp in its steady state condition. These steps are
performed within the inventive battery operated power supply.
[0019] In another preferred embodiment, the ballasting DC-DC
converter is used to drive an array of light emitting diode, or
light emitting crystal, lamps. Preferably, the array consists of
the parallel combination of series-wired groups of lamps. The
output voltage of the DC-DC converter is selected to be slightly
higher than the combined operating voltage of the series
combination of lamps. Each series combination is then configured
with a ballasting device; preferably a resistor, to ensure the
current flowing through each series combination is roughly
equivalent to that of the other groups of lamps.
[0020] The current flowing through the entire array may be
controlled by a MOSFET, or other solid-state switch, such that the
brightness of the array can be controlled. Alternatively, the DC-DC
converter may be operated in a constant current mode such that a
desired electrical current is driven through each series
combination of LED lamps. The brightness can be controlled by
setting the total current produced by the power supply while
operating the lamps in a true flicker-free fashion.
[0021] In another preferred embodiment, each series wired group of
LED lamps is ballasted with an inductor. The brightness can then be
controlled by varying the frequency at which the MOSFET is
operated, thus varying the effective impedance of the inductor.
[0022] In another preferred embodiment, a two-pin constant current
regulator is provided for ballasting an LED lamp, or a series
combination of LED lamps. Preferably the device would be
manufactured to pass a particular current as required for operation
of the lamps. A number of problems associated with the practice of
using resistors to ballast LED lamps are overcome by the inventive
current regulator.
[0023] In yet another preferred embodiment, the inventive DC-DC
converter provides a regulated output higher than the expected
battery voltage. It is well known in the art that to achieve a
particular torque from a DC motor, there is an inverse relationship
between voltage and current. By providing a substantial increase in
the operating voltage of the motor, the motor can employ smaller
wire, experience reduced brush wear, etc. In addition, the
inventive power supply is configured to output a tightly regulated
voltage over a broad range of input voltages. Unlike directly
powering the motor from a battery, or group of batteries, when
driven from the inventive device, the motor will operate with
consistent performance until the battery is essentially completely
discharged.
[0024] In still another preferred embodiment there is provided a
battery including an integral boost or boost/buck regulator such
that, regardless of the application the battery is used in, the
voltage provided by the battery is substantially constant until the
battery itself is discharged to a predetermined voltage.
[0025] Further objects, features, and advantages of the present
invention will be apparent to those skilled in the art upon
examining the accompanying drawings and upon reading the following
description of the preferred embodiments.
BRIEF DESCRIPTION OF DRAWINGS
[0026] FIG. 1 provides a block diagram of a battery operated
lighting system having the inventive power supply.
[0027] FIG. 2 provides a block diagram for a preferred embodiment
of a boost/buck circuit employed in inventive power supply.
[0028] FIG. 3 provides a schematic diagram for an array of LED
lamps which are configured for use with the inventive power
supply.
[0029] FIG. 4 provides a block diagram for a motorized appliance
using the inventive power supply.
[0030] FIG. 5 provides a block diagram for a preferred embodiment
of the inventive power supply which provides a reversing voltage
for a DC motor.
[0031] FIG. 6 provides a schematic diagram for a two-pin
current-regulating device.
[0032] FIG. 7 provides a block diagram of a battery having an
internal regulator to provide a constant voltage throughout the
discharge cycle of the battery.
DETAILED DESCRIPTION
[0033] Before explaining the present invention in detail, it is
important to understand that the invention is not limited in its
application to the details of the construction illustrated and the
steps described herein. The invention is capable of other
embodiments and of being practiced or carried out in a variety of
ways. It is to be understood that the phraseology and terminology
employed herein is for the purpose of description and not of
limitation.
[0034] Referring now to the drawings, wherein like reference
numerals indicate the same parts throughout the several views, a
typical ballasting DC-DC converter for power LED lamps is shown in
FIG. 1. Preferably, converter 100 comprises boost regulator 200 for
powering and ballasting lamp array 300. Generally, converter 100 is
powered by a battery, i.e., battery 108, but may also be powered by
a power supply, for example a wall plug-in type supply.
[0035] Referring to FIG. 2, boost/buck regulator 200 comprises: an
inductor 204; a switching circuit 220 for controlling the current
flowing through inductor 204; a first Schottky diode 206 which
controls the flow of current upon the opening of bucking switch
202; a second Schottky diode 210 which controls the flow of current
upon the opening of boosting switch 208; a capacitor 212 for
filtering the output of regulator 200; a voltage divider 214 which
sets the output voltage of regulator 200; and current sense
resistor 216 and amplifier 218 which provide feedback to circuit
220 of output current. Switching circuit 220 could be constructed
from an integrated switching regulator, discrete components, or a
combination of discrete components and integrated circuits. In a
preferred embodiment, controller 220 comprises a microcontroller
such as the PIC16F819, manufactured by Microchip Technology, Inc.
of Chandler, Ariz., and programmed to monitor the output voltage
and current while operating switches 202 and 208 to maintain proper
conditions at the output. When additional charge is needed at
capacitor 212, switch 202 is operated at progressively higher duty
cycles. When switch 202 approaches 100 per cent duty cycle, circuit
220 begins operating switch 208 to boost the voltage at capacitor
212 to a voltage higher than is available at switch 202.
[0036] Turning next to FIG. 3, LED array 300 comprises a plurality
of light emitting diodes, of which LED lamps 302aa-ag are typical,
configured as a parallel arrangement of series combinations of
light emitting diodes. In a typical configuration, a lighting
device might consist of 20 columns 304a-t of LED lamps wired in
parallel, each column consisting of, for example seven lamps, e.g.,
302aa-ag, wired in series. As will be apparent to those skilled in
the art, the series arrangement of lamps in a column ensures that
each lamp of a column will have the same electrical current flowing
through it as the other lamps of that column. In addition, each
column includes ballasting resister 306a-t to reduce the effects of
slight voltage variations from LED-to-LED and insure the electrical
current will be properly shared between individual columns. Such
ballasting improves the consistency of brightness between
individual LED lamps. As will appreciated by those skilled in the
art, for a particular intensity, the LED lamps of the present
invention operate at a substantially constant voltage and
substantially constant current, unlike LED lamps driven by
tradition pulse width modulation schemes. When used for motion
picture or television filming, driving the LED lamps with a
constant DC power ensures that beating between the filming frame
rate and the LED modulation will never cause flicker, unlike pulse
width modulation schemes.
[0037] Referring to FIGS. 1-3, in operation, the output of battery
108 is applied to boost/buck regulator 200. Preferably, regulator
200 provides an output voltage which can greater than the battery
voltage, less than the battery voltage, or the same as the battery
voltage. The output voltage of regulator 200, which is also the
input voltage to array 300, will remain constant regardless of the
voltage of battery 108, at least within reason. As the output of
regulator 200 is applied to LED array 300, resistors 306a-t provide
ballasting of the current flowing through each series arrangement
of LED lamps.
[0038] By way of example and not limitation, in one preferred
embodiment, the voltage across each LED lamp is approximately 2.7
volts, at 20 milliamps of LED current, and the current flowing
through each LED is controlled over a range from about zero
milliamps through about 20 milliamps. The total current consumed by
the array is measured through current sense resistor 216 and sense
amplifier 218. In a preferred embodiment controller 220 maintains a
constant adjustable current flowing through resistor 216, so long
as the voltage at 214 does not exceed a predetermined maximum
value, the value being roughly equal to the operating voltage of an
LED at maximum current times the number of LED lamps in each series
combination. Thus, for example, assuming 20 milliamps per series
combination and 20 combinations at full brightness the current
would be controlled at 400 milliamps. To dim the LED's the current
is simply maintained at some value between zero and 400 milliamps.
Traditional dimming of LED's is typically performed by pulse width
modulation. Unfortunately in motion picture applications beating
between the PWM frequency and the frame rate can result in
undesirable perceivable flicker in the resulting images, which was
not perceivable to the naked eye.
[0039] It should be noted that as the battery voltage begins to sag
from discharge, preferably regulator 200 compensates to maintain
the proper output voltage, and thus maintain constant brightness of
the lamps, at least to down to battery voltages approaching about 3
volts DC. Accordingly, the inventive circuit allows virtually all
of the charge to be extracted from the battery 108 as opposed to
conventional techniques wherein any drop in battery voltage
produces a corresponding reduction in brightness.
[0040] Turning now to FIG. 6, as is well known in the art, parallel
combinations of LED lamps do not inherently load share well.
Typically the lamp, or string of lamps, with the lowest forward
voltage will hog the current provided for the entire array of lamps
resulting in a group of LED lamps with varying brightness
throughout the group. This problem can be alleviated, at least to
some degree by providing the LED array with a voltage greater than
the required forward voltage for the grouping, and providing a
ballasting device in series with each series combination of LED
lamps. Traditionally a resistor has been employed for this purpose.
Unfortunately, resistors consume energy and therefore reduce the
efficiency of the system. In one preferred embodiment discussed
above, a reactive element, i.e. an inductor was employed to ballast
each string of lamps because the inductor is a storage element,
which returns the energy to the system thereby improving the
efficiency of the system. Unfortunately, neither ballasting
technique completely solves the problem with load sharing and
individual LED lamps in the array may appear brighter, or dimmer,
than their neighboring devices.
[0041] Ideally, a constant current source would be employed for
each series combination of LED lamps. While this technique would
ensure equal current flows in each series combination,
unfortunately it would also consume a great deal of board space and
substantially raise the cost of the board. However, a constant
current ballasting circuit 400 could be used to ensure the proper
current flows through each string of lamps. Circuit 400 could be
reduced to a two terminal device, i.e. terminals 402 and 420, which
is simply wired in series with a string of resistors to provide a
variable voltage drop to control the current flowing therethrough
at a predetermined level. Thus the same constant current of a
predetermined value will flow through every LED in an array, even
if some series-wired groups have more, or less, LED lamps than
others within the array. As will be appreciated by those skilled in
the art, circuit 400 could easily be housed in an industry standard
1206 surface mount package and consume only minimal board
space.
[0042] Circuit 400 comprises a positive first terminal 402
providing external access to the collector 406 of transistor 404
and resistor 412. The opposite end of resistor 412 is connected to
the base 408 of transistor 404. The cathode 416 of Zener diode 414
is also connected to base 408 and the anode 418 is connected to
negative terminal 420. Resistor 422 connects the emitter 410 of
transistor 404 to negative terminal 420. When placed in circuit,
electrical current flows through resistor 412 and zener diode 414
such that the voltage at base 408 will be the same as the reverse
zener voltage of diode 414. As will be apparent to those skilled in
the art, the voltage at emitter 410 will be the voltage at base 408
minus the voltage drop between base 408 and emitter 410 which is a
relative constant value, typically about 0.65 volts. The voltage
across resistor 422 is thus a constant equal to the zener voltage
minus 0.65 volts. Thus it can be seen that the current flowing
through transistor 404 must be defined by the equation:
I.sub.CE=(V.sub.Z-0.65)/R.sub.E
[0043] where:
[0044] I.sub.CE is the current flowing from the collector to the
emitter of transistor 404;
[0045] V.sub.Z is the zener voltage of diode 412; and
[0046] R.sub.E is the resistance of resistor 422.
[0047] Thus, circuit 400 could be integrated into a single package
having two terminals for connection to other circuitry. As will be
appreciated by those skilled in the art, the inventive ballasting
circuit will perform in an identical manner whether: the negative
terminal 420 is connected to ground with positive terminal 402
connected to the cathode of a string of LED lamps; the positive
terminal 402 is connected to the positive voltage supply and
terminal 404 is connected to the anode of a string of LED lamps; or
even if circuit 400 is simply inserted between a pair of lamps in a
series combination of LED lamps.
[0048] While circuit 400 will experience heat producing losses,
like its fixed resistance counterpart, it provides the distinct
advantage over both the resistive and reactive ballasting
techniques in that it forces correct load sharing among the LED
lamps of an array, regardless of the forward voltage of individual
lamps.
[0049] As will be appreciated by those skilled in the art, it can
be seen that the inventive power supply is also well suited for use
with xenon lamps. Like the LED lamps of the previous embodiment, a
characteristic of xenon lamps is that a small change in voltage
results in a comparatively large change in current, hence the need
to provide ballasting. Changes which would tailor the inventive
power supply to a xenon lamp would include: configuring the
regulator 200 to produce a starting voltage of approximately 150
volts prior to igniting the lamp, as will be appreciated by those
skilled in the art, virtually no current is required at this
voltage since the lamp has not been struck; and providing an
igniter circuit of the type presently in use with xenon bulbs. In
other respects, the circuit would function in an identical manner
in that a boost/buck circuit would pre-condition incoming battery
power such that a constant output voltage, or a constant output
current, could be produced over a range of input voltage from about
three volts to about forty volts. Dimming of the lamp can be
effected by varying the frequency of the pulse width modulator,
adjusting the duty cycle of the output of the pulse width
modulator, controlling the output current of regulator 200, or some
combination of these techniques. It should be noted that, unlike
the LED lamps, dimming of a xenon lamp is typically only practical
over a range of approximately one f-stop (e.g., 100% down to 50%) .
To insure proper ballasting, and proper dimming, the range of the
duty cycles produced by the pulse width modulator could be limited,
by way of example and not limitation, to between 35% and 70%,
assuming of course, that dimming was accomplished through pulse
width modulation rather than by varying the output current.
[0050] Referring next to FIG. 4, wherein is shown the inventive
power supply 500 operating in combination with a battery 502 and a
motor 506. Those familiar with battery operated motorized devices
will readily appreciate the advantages of using the inventive power
supply circuit as a power source for a DC motor, the primary
advantages being constant motor speed over a wide range of input
voltages and the ability to extract virtually all of the stored
energy from a battery. As mentioned above, motion picture and
television camcorders are particularly prone to unacceptable speed
variations due to changes in battery voltage. The types of these
devices used for commercial purposes often have separate battery
packs, or sometimes belt batteries worn by the cameraman.
Invariably, while internally these cameras usually have a servo
drive, which provides consistent operation over some range of
voltages, these devices seldom perform well when battery voltage
drops below about 75% of the full charge voltage. In the
entertainment industry, battery management is a major ordeal. While
ballasting is not required for motor applications, by including the
inventive boost regulator 500 between the battery and the camera, a
camera may be operated without degradation from batteries having a
full charge down to approximately three volts. This added range
over which the batteries may operate will reduce the need for spare
batteries, reduce the number of battery changes and, perhaps most
importantly, will reduce the occurrence of problems related to low
voltage when filming.
[0051] Another example of a motorized application for which the
present invention is particularly well suited is a battery operated
electric winch. As will be appreciated by those familiar with such
devices, as the battery discharges, the ability of winch to lift
degrades. This leads to a number of problems, some of which can
actually be dangerous, for example leaving a large heavy object
overhead. When driven by the inventive power supply, performance of
the winch remains constant over virtually the entire discharge
cycle of the battery.
[0052] Yet another example of a battery operated motorized device
is a trolling motor for a fishing boat. Like other motorized
devices, the performance of the trolling motor degrades as the
battery discharges. As a result, a fisherman will typically replace
the battery while substantial charge remains in the battery because
the performance of the motor deteriorates below a reasonable level.
With the present invention, virtually the entire charge can be
extracted from the battery while motor performance remains
constant.
[0053] Yet another advantage to using the inventive power supply
with a trolling motor arises with higher voltage motors. Trolling
motors are often available for use at higher voltages, typically a
multiple of 12 volts (that of a conventional car battery), i.e.,
24, 36, or 48 volts. The advantage being that, for a particular
horsepower, thinner wires can be used reducing the size and weight
of the motor. A fisherman with a higher voltage motor then wires
multiple batteries in series to produce the needed voltage. In such
a system, the battery voltage will fall at a rate determined by the
weakest battery, if one battery goes dead; the fisherman has to
troubleshoot to locate the dead battery.
[0054] In contrast, a fisherman could employ the inventive power
supply adjusted to produce, for example, 48 volts to obtain the
highest performing trolling motor. Batteries could either be used
one-at-a-time or in a series combination. If batteries are used
individually, the system will continue to provide consistent
performance from the motor until the battery voltage approaches
three volts, far below the present usable level. When a battery
goes dead, it is simply replaced by one of the other batteries,
which would have been wired in series under previous schemes. Thus
the fisherman can extract the maximum charge from the combination
of batteries.
[0055] Alternatively, the fisherman could again wire the batteries
in series to produce 48 volts with fresh batteries. As the series
combination discharges, the motor will continue to function
normally until the series combination of the four batteries reaches
approximately three volts. At that time, the fisherman could even
measure each battery and extract the remaining power from any
battery having charge left (assuming that the further discharged
batteries were loading the output of the combination and reducing
the output voltage instead of contributing). In this scheme, the
fisherman would not spend as much time on the water changing
batteries.
[0056] Another advantage to using the inventive power supply with
trolling motors, as well as other motorized devices, is the ease
with which reversing can be accomplished. As will be appreciated by
those skilled in the art, traditionally reversing has been
accomplished either by driving the motor with an H-bridge or by
employing a reversing relay, yet such components are prone to
failure, causing much frustration to end-users and system
designers. The present invention provides an attractive alternative
to either of the prior art solutions in that the inventive power
supply can be configured to selectively produce either a positive
or negative voltage. Turning to FIG. 5, with switches 410 and 414
open, and switch 416 closed, switch 406 can be modulated to control
the current in inductor 412 and thereby provide buck regulation
such that a positive voltage less than or equal to the battery
voltage is presented at motor 406. With switches 406 and 416 closed
and switch 410 open, switch 414 can be modulated to control the
current through inductor 412 and thereby provide boost regulation
such that a positive voltage greater than the battery voltage is
presented at motor 406. With switches 410 and 414 closed and switch
416 open, switch 406 can be modulated to control the current
through inductor 412 and thereby provide negative regulation such
that a negative voltage is presented at motor 406 to reverse the
direction of rotation of motor 406. Capacitors 418 and 420 filter
the output to remove ripple from the output voltage. If polarized
capacitors are used, capacitor 418 is reversed in direction from
capacitor 420 so that one capacitor is properly polarized for
positive regulation and the other capacitor is properly polarized
for negative regulation.
[0057] By way of example and not limitations, other areas, which
could benefit from the inventive power supply include: battery
operated emergency or construction road signs; emergency lighting
systems for buildings; battery operated tools, and other such
systems. It should be noted that boost type regulators typically
operate with efficiency in the range of 85% to 95%. The additional
energy recovered from a battery and the advantage that the system
operates at full performance over the entire discharge cycle far
outweigh losses due to inefficiency.
[0058] Finally, with reference to FIG. 7, the inventive power
supply 200 is exceptionally well suited for incorporation directly
into a rechargeable battery 600, regardless of the application.
When incorporated in battery 600, as the charge is drawn from cell
608, regardless of its chemistry, and its output experiences a
corresponding drop in voltage, boost regulator 200 will act to
regulate the voltage at positive terminal 610 to hold the voltage
at a substantially constant level relative to negative output 612
until cell 608 has been discharged to a predetermined level. It
should be noted that the level of discharge at which the output of
regulator 200 shuts off can be selected to ensure maximum battery
life is obtained. For example, it is generally held that nickel
cadmium batteries will achieve maximum life when the battery is
regularly completely discharged. Accordingly, boost regulator 200
can be configured to operate until cell 608 is virtually exhausted.
It is generally held; on the other hand, that lead acid batteries
achieve maximum life is not entirely discharged. Accordingly, when
used with a lead acid battery, boost regulator 200 can be
configured to shut off output 610 when about 75% of the battery's
capacity has been used. Of course the above examples are provided
by way of example and not limitation and the inventive power supply
can be integrated into the housing of batteries of virtually any
chemistry.
[0059] Recharging can be accomplished by connecting a recharging
voltage across terminals 602 and 604.
[0060] It should also be noted that, while a three-volt dropout has
been discussed with regard to the preferred embodiment, the
invention is not so limited. Depending on the specific design of
the boost regulator, there will always be some non-zero dropout
voltage.
[0061] Thus, the present invention is well adapted to carry out the
objects and attain the ends and advantages mentioned above as well
as those inherent therein. While presently preferred embodiments
have been described for purposes of this disclosure, numerous
changes and modifications will be apparent to those skilled in the
art. Such changes and modifications are encompassed within the
spirit of this invention.
* * * * *